Ignition elements are known per se in diverse construction forms, and are used for initiating the pyrotechnical material safely and at a point in time as defined as possible, or rather to initiate its ignition. The energy for the initiation should be as little as possible.
With respect to the pyrotechnical materials, not only are bursting charges involved, such as for blasting construction works or in mining, but also materials for triggering so-called irreversibly triggerable safety elements in motor vehicles, such as air bags, seat belt temsioning devices and the like. In particular in the case of the latter application, the safe and timewise accurate initiation at an energy expenditure that is as low as possible is of particular importance, ignition faults being safely avoided, in addition.
It is also known that one may position protective circuits and control circuits on the same substrate (cf German Patent No. 37 17 149).
In one typical design, on one substrate an adhesion layer of titanium, for example, is first applied onto which a resistance material such as palladium is applied, as is done, for instance, for integrated circuits. On this resistance material, in turn, a reactive layer made of Zr or Hf, for example, is applied, on which there is provided, in turn, a layer of a reaction partner, such as CuO. This assemblage is generally elongated in a top view and has connecting elements for electrical conductors at the ends. For this purpose, a contact layer such as gold may be applied to the resistance material. These end devices have a comparatively large area in a top view, so that overall there comes about a bridge-like appearance. If an external mechanical or electronic switch is closed, which may also be present on the same substrate, current is able to flow through the bridge section, between the two connecting elements. The resistance layer and the reactive layer present on the resistance layer are thereby heated. The heated reactive layer, in turn, reacts exothermally with the reaction partner, whereby the pyrotechnical material present on this assemblage is initiated. The exothermic reaction achieved in the case of the exemplary construction,Zr+2CuO→ZrO2+Curesults in a reaction enthalpy ΔH=−772 kJ/mol(corresponding to:Zr+O2: ΔH=−1089 kJ/mol,Cu+0.5O2→CuO: ΔH=−157 kJ/mol;Zr+2CuO→Cu+ZrO2: ΔH=−108−(2×−157)=−772 kJ/mol).
Ignition elements of fundamentally the same construction and way of functioning, depending on the kind of materials used, are able also to do, if necessary, without an adhesive and/or a reaction partner; if necessary, the bridge section alone may be formed by a reactive layer.
By contrast, it is the object of the present invention to improve the known ignition element design so that ignition is possible at even low energy input.